Identifying the mechanism of an arrhythmia based on its intracardiac electrograms has become a common challenge to both implantable cardiac defibrillators (ICDs) and the physicians taking care of patients with ICDs. These devices, which are primarily designed to deliver therapy for life-threatening ventricular arrhythmia, frequently deliver inappropriate shocks for a supraventricular tachycardia (SVT). These inappropriate shocks constitute a significant source of physical and emotional distress for patients, cause early ICD battery depletions, and generate a huge financial burden on the health system.
Inappropriate electroshocks from ICDs constitute a significant source of physical and emotional distress on the patients and an unnecessary expense for the health system. Early generations of ICDs operated with an incidence of inappropriate electroshocks as high as 20 to 40%. Tanaka S., An Overview Of Fifth-Generation Implantable Cardioverter Defibrillator, Ann Thorac Cardiovasc Surg., 4:303 311 (1998). Following the introduction of dual-chamber ICDs, however, the overall success for delivering appropriate electroshocks increased to 86 to 100%, while the successful incidence for the treatment of ventricular tachycardias (VT) reached 97 to 100%.
The incidence of inappropriate electroshocks in response to a SVT however, remains a problem. This problem is especially severe for discriminating between a SVT having 1:1 antegrade conduction and a VT having 1:1 retrograde conduction. Thompson et al., Ventriculoatrial Conduction Metrics For Classification Of Ventricular Tachycardia With 1:1 Retrograde Conduction In Dual-Chamber Sensing Implantable Cardioverter Defibrillators, J Electrocardiol., 31:152 156 (1988)
The ability to reduce or avoid all inappropriate electroshocks from ICDs would have a beneficial effect on the physical and emotional state of patients with defibrillators as well as reduce the cost of health care. Clearly, what is needed in the art is a method and a device to prevent the misinterpretation of cardiac electrical signals and avoid the delivery of inappropriate electroshocks. An improved algorithm, based on a patient's baseline cardiac conduction profile as well as automatic updates of that profile, to discriminate between SVT and VT is therefore required.